Multiple light paths architecture and obscuration methods for signal and perfusion index optimization

CROSS REFERENCE TO RELATED APPLICATIONS

0001This application is a continuation of U.S. patent application Ser. No. 14/569,235, filed Dec. 12, 2014 and published on Mar. 3, 2015 as U.S. Patent Publication No. US 2016/0058312. U.S. patent application Ser. No. 14/569,235 claims the benefit under 35 U.S.C. § 119(e) of U.S. Patent Application No. 62/044,515, filed Sep. 2, 2014. The contents of U.S. patent application Ser. No. 14/569,235 and Ser. No. 62/044,515 are incorporated herein by reference in their entirety for all purposes.

FIELD

0002This relates generally to a device that measures a photoplethysmographic (PPG) signal, and, more particularly, to architectures for multiple light paths and obscuration methods for PPG signal and perfusion index optimization.

BACKGROUND

0003A photoplethysmographic (PPG) signal can be measured by PPG systems to derive corresponding physiological signals (e.g., pulse rate). In a basic form, PPG systems can employ a light source or light emitter that injects light into the user's tissue and a light detector to receive light that reflects and/or scatters and exits the tissue. The received light includes light with an amplitude that is modulated as a result of pulsatile blood flow (i.e., “signal”) and parasitic, non-signal light with an amplitude that can be modulated (i.e., “noise” or “artifacts”) and/or unmodulated (i.e., DC). Noise can be introduced by, for example tilt and/or pull of the device relative to the user's tissue, hair, and/or motion.

0004For a given light emitter and light detector, the PPG pulsatile signal (i.e., detected light modulated by pulsatile blood flow) can decrease as the separation distance between the light emitter and light detector increases. On the other hand, perfusion index (i.e., the ratio of pulsatile signal amplitude versus DC light amplitude) can increase as the separation distance between the light emitter and light detector increases. Higher perfusion index tends to result in better rejection of noise due to motion (i.e., rejection of motion artifacts). Therefore, shorter separation distances between a light emitter and a light sensor can favor high PPG signal strength, while longer separation distances can favor high perfusion index (e.g., motion performance). That is, a trade-off can exist, making it difficult to optimize separation distance for particular user skin/tissue types and usage conditions.

0005Additionally, the PPG system can include several light emitters, light detectors, components, and associated wiring that may be visible to a user's eye, making the PPG system aesthetically unappealing.

SUMMARY

0006This relates to a PPG device configured with an architecture suitable for multiple light paths. The architecture can include one or more light emitters and one or more light sensors to generate the multiple light paths for measuring a PPG signal and a perfusion index of a user. The multiple light paths (i.e., the optical paths formed between each pair of light emitter and light detector) can include different locations and/or emitter-to-detector separation distances to generate both an accurate PPG signal and perfusion index value to accommodate a variety of users and a variety of usage conditions. In some examples, the multiple light paths can include different path locations, but the same separation distances along each path. In other examples, the multiple light paths can include overlapping, co-linear paths (i.e., along the same line) but with different emitter-to-detector separation distances along each path. In other examples, the multiple light paths can include different path locations and different emitter-to-detector separation distances along each path. In such examples, the particular configuration of the multiple light paths can be optimized for cancellation of noise due to artifacts resulting from, for example, tilt and/or pull of the device, a user's hair, a user's skin pigmentation, and/or motion. The PPG device can further include one or more lenses and/or reflectors to increase the signal strength and/or and to obscure the light emitters, light sensors, and associated wiring from being visible to a user's eye.

BRIEF DESCRIPTION OF THE DRAWINGS

0007<figref idref="DRAWINGS">FIGS. <b>1</b>A-<b>1</b>C</figref> illustrate systems in which examples of the disclosure can be implemented.

0008<figref idref="DRAWINGS">FIG. <b>2</b></figref> illustrates an exemplary PPG signal.

0009<figref idref="DRAWINGS">FIG. <b>3</b>A</figref> illustrates a top view and <figref idref="DRAWINGS">FIG. <b>3</b>B</figref> illustrates a cross-sectional view of an exemplary electronic device including light sensors and light emitters for determining a heart rate signal.

0010<figref idref="DRAWINGS">FIG. <b>3</b>C</figref> illustrates a flow diagram for canceling or reducing noise from a measured PPG signal.

0011<figref idref="DRAWINGS">FIG. <b>4</b>A</figref> illustrates a top view and <figref idref="DRAWINGS">FIG. <b>4</b>B</figref> illustrates a cross-sectional view of an exemplary device with two light paths for determining a heart rate signal according to examples of the disclosure.

0012<figref idref="DRAWINGS">FIG. <b>5</b>A</figref> illustrates multiple light paths for determining a heart rate signal according to examples of the disclosure.

0013<figref idref="DRAWINGS">FIG. <b>5</b>B</figref> illustrates a plot of PPG signal strength and perfusion index values for multiple light paths with different separation distances according to examples of the disclosure.

0014<figref idref="DRAWINGS">FIG. <b>6</b>A</figref> illustrates a top view of an exemplary electronic device employing multiple light paths for determining a heart rate signal according to examples of the disclosure.

0015<figref idref="DRAWINGS">FIG. <b>6</b>B</figref> illustrates a table of exemplary path lengths, relative PPG signal levels, and relative perfusion index values for an exemplary electronic device employing multiple light paths according to examples of the disclosure.

0016<figref idref="DRAWINGS">FIG. <b>6</b>C</figref> illustrates a cross-sectional view of an exemplary electronic device employing multiple light paths for determining a heart rate signal according to examples of the disclosure.

0017<figref idref="DRAWINGS">FIGS. <b>6</b>D-<b>6</b>F</figref> illustrate cross-sectional views of exemplary electronic devices employing multiple light paths for determining a heart rate signal according to examples of the disclosure.

0018<figref idref="DRAWINGS">FIG. <b>7</b>A</figref> illustrates a top view of an exemplary electronic device with eight light paths for determining a heart rate signal according to examples of the disclosure.

0019<figref idref="DRAWINGS">FIG. <b>7</b>B</figref> illustrates a table of light emitter/sensor paths and separation distances for an exemplary electronic device with eight light paths and four separation distances according to examples of the disclosure.

0020<figref idref="DRAWINGS">FIG. <b>7</b>C</figref> illustrates a plot of PPG signal strength and perfusion index values for an exemplary architecture with eight light paths and four separation distances according to examples of the disclosure.

0021<figref idref="DRAWINGS">FIGS. <b>7</b>D-<b>7</b>F</figref> illustrate cross-sectional views of exemplary electronic devices employing one or more light paths for determining a heart rate signal according to examples of the disclosure.

0022<figref idref="DRAWINGS">FIG. <b>8</b></figref> illustrates an exemplary block diagram of a computing system comprising light emitters and light sensors for measuring a PPG signal according to examples of the disclosure.

0023<figref idref="DRAWINGS">FIG. <b>9</b></figref> illustrates an exemplary configuration in which a device is connected to a host according to examples of the disclosure.

DETAILED DESCRIPTION

0024In the following description of examples, reference is made to the accompanying drawings in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the various examples.

0025Various techniques and process flow steps will be described in detail with reference to examples as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects and/or features described or referenced herein. It will be apparent, however, to one skilled in the art, that one or more aspects and/or features described or referenced herein may be practiced without some or all of these specific details. In other instances, well-known process steps and/or structures have not been described in detail in order to not obscure some of the aspects and/or features described or referenced herein.

0026Further, although process steps or method steps can be described in a sequential order, such processes and methods can be configured to work in any suitable order. In other words, any sequence or order of steps that can be described in the disclosure does not, in and of itself, indicate a requirement that the steps be performed in that order. Further, some steps may be performed simultaneously despite being described or implied as occurring non-simultaneously (e.g., because one step is described after the other step). Moreover, the illustration of a process by its depiction in a drawing does not imply that the illustrated process is exclusive of other variations and modification thereto, does not imply that the illustrated process or any of its steps are necessary to one or more of the examples, and does not imply that the illustrated process is preferred.

0027A photoplethysmographic (PPG) signal can be measured by PPG systems to derive corresponding physiological signals (e.g., pulse rate). Such PPG systems can be designed to be sensitive to changes in blood in a user's tissue that can result from fluctuations in the amount or volume of blood or blood oxygen contained in a vasculature of the user. In a basic form, PPG systems can employ a light source or light emitter that injects light into the user's tissue and a light detector to receive light that reflects and/or scatters and exits the tissue. The PPG signal is the amplitude of the reflected and/or scattered light that is modulated with volumetric change in blood volume in the tissue. However, the PPG signal may be compromised by noise due to artifacts. Artifacts resulting from, for example, tilt and/or pull of the device relative to the user's tissue, hair, and/or motion can introduce noise into the signal. For example, the amplitude of reflected light can modulate due to the motion of the user's hair. As a result, the amplitude modulation of the reflected light caused by hair motion can be erroneously interpreted as a result of pulsatile blood flow.

0028This disclosure relates to a multiple light paths architecture and obscuration methods for PPG signal and perfusion index optimization. The architecture can include one or more light emitters and one or more light sensors to generate the multiple light paths to measure a PPG signal and a perfusion index of a user. The multiple light paths can include different locations and/or separation distances between light emitters and light detectors to generate both an accurate PPG signal and perfusion index value to accommodate a variety of users and a variety of usage conditions. In some examples, the multiple light paths can include different path locations, but the same emitter-to-detector separation distances along each path. In some examples, the multiple light paths can include overlapping, co-linear paths (i.e., along the same line), but with different emitter-to-separation distances along each other. In some examples, the multiple light paths can include different path locations and different emitter-to-detector separation distances along each path. In such examples, the particular configuration of the multiple light paths is optimized for noise cancellation due to artifacts such as tilt and/or pull of the device, a user's hair, a user's skin pigmentation, and/or motion. In some examples, the device can include one or more lenses and/or reflectors to increase the signal strength and/or to obscure the light emitters, light sensors, and associated wiring from being visible to a user's eye.

0029Representative applications of methods and apparatus according to the present disclosure are described in this section. These examples are being provided solely to add context and aid in the understanding of the described examples. It will thus be apparent to one skilled in the art that the described examples may be practiced without some or all of the specific details. In other instances, well-known process steps have been described in detail in order to avoid unnecessarily obscuring the described examples. Other applications are possible, such that the following examples should not be taken as limiting.

0030<figref idref="DRAWINGS">FIGS. <b>1</b>A-<b>1</b>C</figref> illustrate systems in which examples of the disclosure can be implemented. <figref idref="DRAWINGS">FIG. <b>1</b>A</figref> illustrates an exemplary mobile telephone <b>136</b> that can include a touch screen <b>124</b>. <figref idref="DRAWINGS">FIG. <b>1</b>B</figref> illustrates an exemplary media player <b>140</b> that can include a touch screen <b>126</b>. <figref idref="DRAWINGS">FIG. <b>1</b>C</figref> illustrates an exemplary wearable device <b>144</b> that can include a touch screen <b>128</b> and can be attached to a user using a strap <b>146</b>. The systems of <figref idref="DRAWINGS">FIGS. <b>1</b>A-<b>1</b>C</figref> can utilize the multiple light path architectures and obscuration methods as will be disclosed.

0031<figref idref="DRAWINGS">FIG. <b>2</b></figref> illustrates an exemplary PPG signal. A user's PPG signal absent of artifacts is illustrated as signal <b>210</b>. However, movement of the body of the user can cause the skin and vasculature to expand and contract, introducing noise to the signal. Additionally, a user's hair and/or tissue can change the amplitude of light reflected and the amplitude of light absorbed. A user's PPG signal with artifacts is illustrated as signal <b>220</b>. Without extraction of noise, signal <b>220</b> can be misinterpreted.

0032Signal <b>210</b> can include light information with an amplitude that is modulated as a result of pulsatile blood flow (i.e., “signal”) and parasitic, unmodulated, non-signal light (i.e., DC). From the measured PPG signal <b>210</b>, a perfusion index can be determined. The perfusion index can be the ratio of received modulated light (ML) to unmodulated light (UML) (i.e., ratio of blood flow modulated signal to static, parasitic DC signal) and can give extra information regarding the user's physiological state. The modulated light (ML) can be the peak-to-valley value of signal <b>210</b>, and unmodulated light (UML) can be the zero-to-average (using average <b>212</b>) value of signal <b>210</b>. As shown in <figref idref="DRAWINGS">FIG. <b>2</b></figref>, the perfusion index can be equal to the ratio of ML to UML.

0033Both the PPG signal and perfusion index can be related to an accurate measurement of physiological signals such as heart rate. However, the PPG signal can include noise from modulated light resulting from, for example, motion of the user's tissue and/or the PPG device. Higher perfusion index (e.g., higher pulsatile signal and/or lower parasitic DC) can result in better rejection of such motion noise. Additionally, the intensity of a PPG signal relative to perfusion index can vary for different users. Some users may naturally have a high PPG signal, but a weak perfusion index or vice versa. Thus, the combination of PPG signal and perfusion index can be used to determine physiological signals for a variety of users and a variety of usage conditions.

0034<figref idref="DRAWINGS">FIG. <b>3</b>A</figref> illustrates a top view and <figref idref="DRAWINGS">FIG. <b>3</b>B</figref> illustrates a cross-sectional view of an exemplary electronic device including light sensors and light emitters for determining a heart rate signal. A light sensor <b>304</b> can be located with a light emitter <b>306</b> on a surface of device <b>300</b>. Additionally, another light sensor <b>314</b> can be located or paired with light emitter <b>316</b> on a surface of device <b>300</b>. Device <b>300</b> can be situated such that light sensors <b>304</b> and <b>314</b> and light emitters <b>306</b> and <b>316</b> are proximate to a skin <b>320</b> of a user. For example, device <b>300</b> can be held in a user's hand or strapped to a user's wrist, among other possibilities.

0035Light emitter <b>306</b> can generate light <b>322</b>. Light <b>322</b> can be incident on skin <b>320</b> and can reflect back to be detected by light sensor <b>304</b>. A portion of light <b>322</b> can be absorbed by skin <b>320</b>, vasculature, and/or blood, and a portion of light (i.e., light <b>332</b>) can be reflected back to light sensor <b>304</b> located or paired with light emitter <b>306</b>. Similarly, light emitter <b>316</b> can generate light <b>324</b>. Light <b>324</b> can be incident on skin <b>320</b> and can reflect back to be detected by light sensor <b>314</b>. A portion of light <b>324</b> can be absorbed by skin <b>320</b>, vasculature, and/or blood, and a portion of light (i.e., light <b>334</b>) can be reflected back to light sensor <b>314</b> located with light emitter <b>316</b>. Light <b>332</b> and <b>334</b> can include information or signals such as a heart rate signal (i.e., PPG signal) due to a blood pulse wave <b>326</b>. Due to a distance between light sensors <b>304</b> and <b>314</b> along the direction of the blood pulse wave <b>326</b>, signal <b>332</b> can include a heart rate signal, whereas signal <b>334</b> can include a time-shifted heart rate signal. A difference between signal <b>332</b> and signal <b>334</b> can depend on the distance between light sensors <b>304</b> and <b>314</b> and the velocity of blood pulse wave <b>326</b>.

0036Signals <b>332</b> and <b>334</b> can include noise <b>312</b> due to artifacts resulting from, for example, tilt and/or pull of device <b>300</b> relative to skin <b>320</b>, a user's hair, and/or a user's motion. One way to account for noise <b>312</b> can be to locate light sensors <b>304</b> and <b>314</b> far enough such that noise in signals <b>332</b> and <b>334</b> may be uncorrelated, but close enough together that PPG signal is corrected in signals <b>332</b> and <b>334</b>. The noise can be mitigated by scaling, multiplying, dividing, adding, and/or subtracting signals <b>332</b> and <b>334</b>.

0037<figref idref="DRAWINGS">FIG. <b>3</b>C</figref> illustrates a flow diagram for canceling or reducing noise from a measured PPG signal. Process <b>350</b> can include light emitted from one or more light emitters <b>306</b> and <b>316</b> (step <b>352</b>) located on a surface of device <b>300</b>. Light information <b>332</b> can be received by light sensor <b>304</b> (step <b>354</b>), and light information <b>334</b> can be received by light sensor <b>314</b> (step <b>356</b>). In some examples, light information <b>332</b> and <b>334</b> can indicate an amount of light from light emitters <b>306</b> and <b>316</b> that has been reflected and/or scattered by skin <b>320</b>, blood, and/or vasculature of the user. In some examples, light information <b>332</b> and <b>334</b> can indicate an amount of light that has been absorbed by skin <b>320</b>, blood, and/or vasculature of the user.

0038Based on light information <b>332</b> and light information <b>334</b>, a heart rate signal can be computed by canceling noise due to artifacts (step <b>358</b>). For example, light information <b>334</b> can be multiplied by a scaling factor and added to light information <b>332</b> to obtain the heart rate signal. In some examples, heart rate signal can be computed by merely subtracting or dividing light information <b>334</b> from light information <b>332</b>.

0039In some examples, light information <b>332</b> and <b>334</b> can be difficult to determine due to a low signal intensity. To increase the signal intensity or signal strength, the distance between light sensors and light emitters can be reduced or minimized such that light travels the shortest distance. Generally, for a given light emitter and light sensor pair, the signal strength decreases with increasing separation distance between the light emitter and light sensor. On the other hand, the perfusion index generally increases with increasing separation distance between the light emitter and the light sensor. A higher perfusion index can correlate to better rejection of artifacts caused by, for example, motion. Therefore, shorter separation distances between a light emitter and a light sensor can favor high PPG signal strength, while longer separation distances can favor high perfusion index (e.g., motion performance). That is, a trade-off can exist making it difficult to optimize separation distance for particular user skin/tissue types and usage conditions.

0040To alleviate the trade-off issue between signal strength and perfusion index, multiple light paths with various distances between light emitter(s) and light sensor(s) can be employed. <figref idref="DRAWINGS">FIG. <b>4</b>A</figref> illustrates a top view and <figref idref="DRAWINGS">FIG. <b>4</b>B</figref> illustrates a cross-sectional view of an exemplary device with two light paths for determining a heart rate signal according to examples of the disclosure. Device <b>400</b> can include light emitters <b>406</b> and <b>416</b> and a light sensor <b>404</b>. Light emitter <b>406</b> can have a separation distance <b>411</b> from light sensor <b>404</b>, and light emitter <b>416</b> can have a separation distance <b>413</b> from light sensor <b>404</b>.

0041Light <b>422</b> from light emitter <b>406</b> can be incident on skin <b>420</b> and can reflect back as light <b>432</b> to be detected by light sensor <b>404</b>. Similarly, light <b>424</b> from light emitter <b>416</b> can be incident on skin <b>420</b> and can reflect back as light <b>434</b> to be detected by light sensor <b>404</b>. Separation distance <b>411</b> can be small compared to separation distance <b>413</b>, and as a result, light information <b>432</b> can have a higher PPG signal strength than light information <b>434</b>. Light information <b>432</b> can be employed for applications requiring a higher PPG signal strength. Separation distance <b>413</b> can be large compared to separation distance <b>411</b>, and as a result, light information <b>434</b> can have a higher perfusion index than light information <b>432</b>. Light information <b>434</b> can be employed for applications requiring a high perfusion index (e.g., motion performance). Due to the different separation distances <b>411</b> and <b>413</b>, light information <b>432</b> and <b>434</b> can provide various combinations of PPG signals and perfusion index values to allow the device to dynamically select light information for particular user skin types and usage conditions (e.g., sedentary, active motion, etc.).

0042<figref idref="DRAWINGS">FIG. <b>5</b>A</figref> illustrates multiple light paths for determining a heart rate signal according to examples of the disclosure. For enhanced measurement resolution, more than two light paths can be employed. Multiple light paths can be formed from a light emitter <b>506</b> and a plurality of light sensors such as light sensors <b>504</b>, <b>514</b>, <b>524</b>, <b>534</b>, and <b>544</b>. Light sensor <b>504</b> can have a separation distance <b>511</b> from light emitter <b>506</b>. Light sensor <b>514</b> can have a separation distance <b>513</b> from light emitter <b>506</b>. Light sensor <b>524</b> can have a separation distance <b>515</b> from light emitter <b>506</b>. Light sensor <b>534</b> can have a separation distance <b>517</b> from light emitter <b>506</b>. Light sensor <b>544</b> can have a separation distance <b>519</b> from light emitter <b>506</b>. Separation distances <b>511</b>, <b>513</b>, <b>515</b>, <b>517</b>, and <b>519</b> can be different values.

0043<figref idref="DRAWINGS">FIG. <b>5</b>B</figref> illustrates a plot of PPG signal strength and perfusion index values for light emitter <b>506</b> and light sensors <b>504</b>, <b>514</b>, <b>524</b>, <b>534</b>, and <b>544</b>. As shown, an intensity of the PPG signal or signal strength can decrease as the separation distance between a light emitter and a light sensor (i.e., separation distances <b>511</b>, <b>513</b>, <b>515</b>, <b>517</b>, and <b>519</b>) increases. On the other hand, the perfusion index value can increase as the separation distance between a light emitter and a light sensor increases.

0044Information obtained from the multiple light paths can be used both for applications requiring a high PPG signal strength and applications requiring a high perfusion index value. In some examples, information generated from all light paths can be utilized. In some examples, information generated from some, but not all light paths can be utilized. In some examples, the “active” light paths can be dynamically changed based on the application(s), available power, user type, and/or measurement resolution.

0045<figref idref="DRAWINGS">FIG. <b>6</b>A</figref> illustrates a top view and <figref idref="DRAWINGS">FIG. <b>6</b>C</figref> illustrates a cross-sectional view of an exemplary electronic device employing multiple light paths for determining a heart rate signal according to examples of the disclosure. Device <b>600</b> can include light emitters <b>606</b> and <b>616</b> and light sensors <b>604</b> and <b>614</b> located on a surface of device <b>600</b>. Light sensors <b>604</b> and <b>614</b> can be symmetrically placed, while light emitters <b>606</b> and <b>616</b> can be asymmetrically placed. Optical isolation <b>644</b> can be disposed between light emitters <b>606</b> and <b>616</b> and light detectors <b>604</b> and <b>614</b>. In some examples, optical isolation <b>644</b> can be an opaque material to, for example, reduce parasitic DC light.

0046Light emitters <b>606</b> and <b>616</b> and light sensors <b>604</b> and <b>614</b> can be mounted on or touching component mounting plane <b>648</b>. In some examples, component mounting plane <b>648</b> can be made of an opaque material (e.g., flex). In some examples, component mounting plane <b>648</b> can be made of a same material as optical isolation <b>644</b>.

0047Device <b>600</b> can include windows <b>601</b> to protect light emitters <b>606</b> and <b>616</b> and light sensors <b>604</b> and <b>614</b>. Light emitters <b>606</b> and <b>616</b>, light detectors <b>604</b> and <b>614</b>, optical isolation <b>644</b>, component mounting plane <b>648</b>, and windows <b>601</b> can be located within an opening <b>603</b> of housing <b>610</b>. In some examples, device <b>600</b> can be a wearable device such as a wristwatch, and housing <b>610</b> can be coupled to a wrist strap <b>646</b>.

0048Light emitters <b>606</b> and <b>616</b> and light detectors <b>604</b> and <b>614</b> can be arranged such that there are four light paths with four different separation distances. Light path <b>621</b> can be coupled to light emitter <b>606</b> and light sensor <b>604</b>. Light path <b>623</b> can be coupled to light emitter <b>606</b> and light sensor <b>614</b>. Light path <b>625</b> can be coupled to light emitter <b>616</b> and light sensor <b>614</b>. Light path <b>627</b> can be coupled to light emitter <b>616</b> and light sensor <b>604</b>.

0049<figref idref="DRAWINGS">FIG. <b>6</b>B</figref> illustrates a table of exemplary path lengths, relative PPG signals levels, and relative perfusion index values for light paths <b>621</b>, <b>623</b>, <b>625</b>, and <b>627</b> of device <b>600</b> according to examples of the disclosure. As shown, relative PPG signal levels can have higher values for shorter path lengths. For example, light path <b>625</b> can have a higher PPG signal of 1.11 than light path <b>627</b> with a PPG signal of 0.31 due to the shorter path length (i.e., path length of light path <b>625</b> is 4.944 mm, whereas path length of light path <b>627</b> is 6.543 mm). For applications that require high PPG signal levels, device <b>600</b> can utilize information from light path <b>625</b> or light path <b>621</b>. However, relative perfusion index values can have higher values for longer path lengths. For example, light path <b>623</b> can have a higher perfusion index value of 1.23 than light path <b>621</b> with a perfusion index value of 1.10 due to the longer path length (e.g., path length of light path <b>623</b> is 5.915 mm, whereas path length of light path <b>621</b> is 5.444 mm). For applications that require high perfusion index values, device <b>600</b> can favor information from light path <b>623</b> over information from light path <b>621</b>. While <figref idref="DRAWINGS">FIG. <b>6</b>B</figref> illustrates exemplary values for path lengths <b>621</b>, <b>623</b>, <b>625</b>, and <b>627</b> along with exemplary PPG signal levels and perfusion index values, examples of the disclosure are not limited to these values.

0050<figref idref="DRAWINGS">FIGS. <b>6</b>D-<b>6</b>F</figref> illustrate cross-sectional views of exemplary electronic devices employing multiple light paths for determining a heart rate signal according to examples of the disclosure. As shown in <figref idref="DRAWINGS">FIG. <b>6</b>D</figref>, optical isolation <b>654</b> can be designed to improve mechanical stability of device <b>600</b> by providing a larger surface area (than optical isolation <b>644</b> of <figref idref="DRAWINGS">FIG. <b>6</b>C</figref>) for windows <b>601</b> to rest on and/or adhere to. While optical isolation <b>654</b> can provide a larger surface area for windows <b>601</b>, the light may have to travel a longer distance through skin <b>620</b>, and as a result, the signal intensity may be reduced. Either the signal quality can be compromised or device <b>600</b> can compensate by increasing the power (i.e., battery power consumption) of light emitted from light emitter <b>606</b>. A lower signal intensity or a higher battery power consumption can degrade the user's experience.

0051One way to overcome the issues with lower signal intensity and higher power consumption can be illustrated in <figref idref="DRAWINGS">FIG. <b>6</b>E</figref>. Device <b>600</b> can include lens <b>609</b> coupled to light emitter <b>606</b> and/or lens <b>605</b> coupled to light sensor <b>604</b>. Lens <b>609</b> can be any type of lens such as a Fresnel lens or image displacement film (IDF) that steers the light over the optical isolation <b>644</b>. Lens <b>605</b> can be any type of lens such as an IDF or a brightness enhancement film (BEF) that shifts the light into an optical receiving area of light sensor <b>604</b>. Lens <b>609</b> can direct light emitted from light emitter <b>606</b> closer to lens <b>605</b>, and lens <b>605</b> can direct light to closer light sensor <b>604</b>. By employing lenses <b>609</b> and/or <b>605</b>, light may not have to travel a longer distance through skin <b>620</b>, and as a result, the signal intensity can be recovered.

0052In some examples, device <b>600</b> can include a reflector <b>607</b>, in addition to or alternatively to lens <b>609</b> and <b>605</b>, as shown in <figref idref="DRAWINGS">FIG. <b>6</b>F</figref>. Reflector <b>607</b> can be formed from any reflective material such as a mirror or a white surface. Light emitted from light emitter <b>606</b> can reflect off the surface of skin <b>620</b> and be directed back to reflector <b>607</b>. Such light in the architectures illustrated in <figref idref="DRAWINGS">FIGS. <b>6</b>D-<b>6</b>E</figref> could be lost or absorbed by optical isolation <b>654</b>. However, in the architecture illustrated in <figref idref="DRAWINGS">FIG. <b>6</b>F</figref>, reflector <b>607</b> can prevent light loss by reflecting the light back to skin <b>620</b>, and the light could then be reflected to light sensor <b>604</b>. In some examples, optical isolation <b>654</b> can include any number of reflectors <b>607</b>. In some examples, one or more windows <b>601</b> can include any number of reflectors <b>607</b>.

0053<figref idref="DRAWINGS">FIG. <b>7</b>A</figref> illustrates a top view of an exemplary electronic device with multiple light paths for determining a heart rate signal according to examples of the disclosure. Device <b>700</b> can include a plurality of light emitters <b>706</b> and <b>716</b> and a plurality of light sensors <b>704</b>, <b>714</b>, <b>724</b>, and <b>734</b> located on a surface of device <b>700</b>. Optical isolation <b>744</b> can be disposed between light emitters <b>706</b> and <b>716</b> and light sensors <b>704</b>, <b>714</b>, <b>724</b>, and <b>734</b> to prevent light mixing. Component mounting plane <b>748</b> can be mounted behind light emitters <b>706</b> and <b>716</b> and light sensors <b>704</b>, <b>714</b>, <b>724</b>, and <b>734</b>. Windows such as window <b>701</b> can be located in front of light emitters <b>706</b> and <b>716</b> and light sensors <b>704</b>, <b>714</b>, <b>724</b>, and <b>734</b> for protection. The plurality of light emitters <b>706</b> and <b>716</b>, plurality of light detectors <b>704</b>, <b>714</b>, <b>724</b>, and <b>734</b>, optical isolation <b>744</b>, component mounting plane <b>748</b>, and windows <b>701</b> can be located within an opening <b>703</b> of housing <b>710</b>. In some examples, device <b>700</b> can be a wearable device such as a wristwatch, and housing <b>710</b> can be coupled to a wrist strap <b>746</b>.

0054Although <figref idref="DRAWINGS">FIG. <b>7</b>A</figref> illustrates two light emitters and four light sensors, any number of light emitters and light sensors can be employed. In some examples, light sensors <b>704</b> and <b>724</b> can be a single light sensor partitioned into two or more separate sensing regions. Similarly, light sensors <b>714</b> and <b>734</b> can be a single light sensor partitioned into two or more separate sensing regions. In some examples, optical isolation <b>744</b> and/or component mounting plane <b>748</b> can be an opaque material. In some examples, one or more of optical isolation <b>744</b>, component mounting plane <b>748</b>, and housing <b>710</b> can be a same material.

0055Light emitters <b>706</b> and <b>716</b> and light sensors <b>704</b>, <b>714</b>, <b>724</b>, and <b>734</b> can be arranged such that there are eight light paths with four different path lengths or separation distances. Light path <b>721</b> can be coupled to light emitter <b>706</b> and light sensor <b>704</b>. Light path <b>723</b> can be coupled to light emitter <b>706</b> and light sensor <b>734</b>. Light path <b>725</b> can be coupled to light emitter <b>706</b> and light sensor <b>714</b>. Light path <b>727</b> can be coupled to light emitter <b>716</b> and light sensor <b>734</b>. Light path <b>729</b> can be coupled to light emitter <b>716</b> and light sensor <b>714</b>. Light path <b>731</b> can be coupled to light emitter <b>716</b> and light sensor <b>724</b>. Light path <b>733</b> can be coupled to light emitter <b>716</b> and light sensor <b>704</b>. Light path <b>735</b> can be coupled to light emitter <b>706</b> and light sensor <b>724</b>.

0056Light emitters <b>706</b> and <b>716</b> and light sensors <b>704</b>, <b>714</b>, <b>724</b>, and <b>734</b> can be placed such that the separation distances of light paths <b>721</b> and <b>729</b> (i.e., separation distance d1) are the same, the separation distances of light paths <b>727</b> and <b>735</b> (i.e., separation distance d2) are the same, the separation distances of light paths <b>723</b> and <b>731</b> (i.e., separation distance d3) are the same, and the separation distances of light paths <b>725</b> and <b>733</b> (i.e., separation distance d4) are the same. In some examples, two or more of the light paths can be overlapping light paths. In some examples, two or more of the light paths can be non-overlapping light paths. In some examples, two or more light paths can be co-located light paths. In some examples, two or more light paths can be non-co-located light paths.

0057An advantage to the multiple light-path architecture illustrated in <figref idref="DRAWINGS">FIG. <b>7</b>A</figref> can be signal optimization. There can be non-overlapping lights paths such that if there is signal loss in one light path, other light paths can be used for signal redundancy. That is, the device can ensure the existence of a signal by having light paths that collectively span a larger total area. The architecture can mitigate against the risk of having only one light path where signal is either very low or non-existent. A very low or non-existent signal can render a light path ineffective due to, for example, a user's particular physiology where a “quiet” no-signal (or low signal) spot exists. For example, light path <b>729</b> can be used for signal redundancy when there is signal loss in light path <b>721</b>.

0058<figref idref="DRAWINGS">FIG. <b>7</b>B</figref> illustrates a table of light emitter/sensor paths and separation distances for an exemplary electronic device with eight light paths and four separation distances according to examples of the disclosure. <figref idref="DRAWINGS">FIG. <b>7</b>C</figref> illustrates a plot of PPG signal strength and perfusion index values for an exemplary architecture with eight light paths and four separation distances according to examples of the disclosure. As shown, an intensity of the PPG signal can decrease as the separation distance between a light emitter and a light sensor (i.e., separation distances d1, d2, d3, and d4) increases. On the other hand, the perfusion index value can increase as the separation distance between a light emitter and a light sensor increases.

0059By configuring the light sensors and light emitters such that multiple light paths have a same separation distance, noise due to artifacts such as motion, user hair and user skin can be canceled or reduced. For example, light path <b>721</b> and light path <b>729</b> can be two different light paths with a same separation distance d1. Due to the separation distance being the same for both light paths, the PPG signal should be the same. However, light path <b>721</b> can reflect off a different area of the user's skin, vasculature, and blood than light path <b>729</b>. Due to the asymmetry of the human skin, vasculature, and blood, light information from light path <b>721</b> can be different than light information from light path <b>729</b>. For example, a user's skin pigmentation in light path <b>721</b> can be different than the user's skin pigmentation in light path <b>729</b>, leading to a different signal for light path <b>721</b> and light path <b>729</b>. Such differences in light information can be used to cancel or reduce noise and/or enhance pulsatile signal quality to determine an accurate PPG signal.

0060In some examples, light emitters <b>706</b> and <b>716</b> can be different light sources. Exemplary light sources can include, but are not limited to, light emitting diodes (LEDs), incandescent lights, and fluorescent lights. In some examples, light emitters <b>706</b> and <b>716</b> can have different emission wavelengths. For example, light emitter <b>706</b> can be a green LED and light emitter <b>716</b> can be an infrared (IR) LED. A user's blood can effectively absorb light from a green light source, and thus, the light path coupled to light emitter <b>706</b> with the shortest separation distance (i.e., light path <b>721</b>) can be used for a high PPG signal when a user is sedentary, for example. An IR light source can effectively travel further distances through a user's skin than other light sources and as a result, can consume less power. A light path coupled to light emitter <b>716</b> (i.e., light paths <b>727</b>, <b>729</b>, <b>731</b>, and <b>733</b>) can be used when device <b>700</b> is operating in a low power mode, for example. In some examples, light emitters <b>706</b> and <b>716</b> can have different emission intensities.

0061<figref idref="DRAWINGS">FIGS. <b>7</b>D-<b>7</b>F</figref> illustrate cross-sectional views of exemplary electronic devices employing one or more light paths for determining a heart rate signal according to examples of the disclosure. Device <b>700</b> can include window <b>701</b> located in front of a component such as light emitter <b>706</b> of <figref idref="DRAWINGS">FIG. <b>7</b>D</figref> and light sensor <b>704</b> of <figref idref="DRAWINGS">FIG. <b>7</b>E</figref>. Window <b>701</b> may be transparent, and as a result, the internal components of device <b>700</b> may be visible to a user. Since device <b>700</b> can include several components and associated wiring, it can be desirable to obscure the components and prevent internal components from being visible to a user's eye. In addition to obscuring the internal components, it may be desirable that the light emitted from light emitter <b>706</b> retains its optical power, collection efficiency, beam shape, and collection area so that the intensity of light is unaffected.

0062To obscure internal components, a lens such as a Fresnel lens <b>707</b> can be located between window <b>701</b> and light emitter <b>706</b>, as shown in <figref idref="DRAWINGS">FIG. <b>7</b>D</figref>. Fresnel lens <b>707</b> can have two regions: an optical center <b>709</b> and a cosmetic zone <b>711</b>. Optical center <b>709</b> can be placed in substantially a same area or location as light emitter <b>706</b> to collimate the emitted light into a smaller beam size. Cosmetic zone <b>711</b> can be located in areas outside of optical center <b>709</b>. The ridges of the cosmetic zone <b>709</b> can act to obscure the underlying internal components.

0063To obscure light sensor <b>704</b>, a lens such as Fresnel lens <b>713</b> can be located between window <b>701</b> and light sensor <b>704</b>, as shown in <figref idref="DRAWINGS">FIG. <b>7</b>E</figref>. Because light sensor <b>704</b> can be a large-area photodiode, shaping of the light field may not be needed, so Fresnel lens <b>713</b> may not require an optical center. Instead, Fresnel lens <b>713</b> may have one region comprising ridges configured for a cosmetic zone.

0064The ridge shapes of Fresnel lenses <b>707</b> and <b>713</b> can be altered to improve obscuration, especially in cosmetic zones. For example, deep and sharp sawtooth patterns can be used for high obscuration needs. Other types of ridge shapes can include rounded cylindrical ridges, asymmetric shapes, and wavy shapes (i.e., ridges that move in and out).

0065In some examples, the Fresnel lens <b>707</b> illustrated in <figref idref="DRAWINGS">FIG. <b>7</b>D</figref> can be used additionally or alternatively for light collimation. By collimating light, the optical signal efficiency can be improved. Without a lens or similar collimating optical element, emitter light can be directed at an angle away from the light sensor and can be lost. Additionally or alternatively, light can be directed at an angle toward the light sensor, but the angle may be shallow. The shallow angle may prevent the light from penetrating deep enough to reach the signal layers in the skin. This light may contribute only to parasitic, non-signal light. The Fresnel lens <b>707</b> can redirect light to directions that otherwise may be lost or enter into the tissue at shallow angles. Such redirected light can be collected instead of being lost and/or can mitigate against parasitic non-signal light, resulting in improved optical signal efficiency.

0066In some examples, a diffusing agent can be used. Diffusing agent <b>719</b> can be surrounding, touching, and/or covering one or more components of light emitter <b>706</b>. In some examples, diffusing agent <b>719</b> can be a resin or epoxy that encapsulates the dies or components and/or wire bonds. Diffusing agent <b>719</b> can be used to adjust the angle of the light emitted from light emitter <b>706</b>. For example, the angle of light emitted from a light emitter without a diffusing agent can be 5° wider than the angle of light emitter from light emitter <b>706</b> encapsulated by diffusing agent <b>719</b>. By narrowing the beam of light emitted, more light can be collected by the lens and/or window resulting in a larger amount of detected light by the light sensor.

0067In some examples, diffusing agent <b>719</b> can have an increased reflectivity for the wavelength or color of emitted light from light emitter <b>706</b>. For example, if light emitter <b>706</b> emits green light, diffusing agent <b>719</b> can be made of white TiO₂material to increase the amount of green light reflected back toward the skin. This way, light that would have otherwise been lost can be recycled back and detected by the light detector.

0068<figref idref="DRAWINGS">FIG. <b>8</b></figref> illustrates an exemplary block diagram of a computing system comprising light emitters and light sensors for measuring a PPG signal according to examples of the disclosure. Computing system <b>800</b> can correspond to any of the computing devices illustrated in <figref idref="DRAWINGS">FIGS. <b>1</b>A-<b>1</b>C</figref>. Computing system <b>800</b> can include a processor <b>810</b> configured to execute instructions and to carry out operations associated with computing system <b>800</b>. For example, using instructions retrieved from memory, processor <b>810</b> can control the reception and manipulation of input and output data between components of computing system <b>800</b>. Processor <b>810</b> can be a single-chip processor or can be implemented with multiple components.

0069In some examples, processor <b>810</b> together with an operating system can operate to execute computer code and produce and use data. The computer code and data can reside within a program storage block <b>802</b> that can be operatively coupled to processor <b>810</b>. Program storage block <b>802</b> can generally provide a place to hold data that is being used by computing system <b>800</b>. Program storage block <b>802</b> can be any non-transitory computer-readable storage medium, and can store, for example, history and/or pattern data relating to PPG signal and perfusion index values measured by one or more light sensors such as light sensor <b>804</b>. By way of example, program storage block <b>802</b> can include Read-Only Memory (ROM) <b>818</b>, Random-Access Memory (RAM) <b>822</b>, hard disk drive <b>808</b> and/or the like. The computer code and data could also reside on a removable storage medium and loaded or installed onto the computing system <b>800</b> when needed. Removable storage mediums include, for example, CD-RM, DVD-ROM, Universal Serial Bus (USB), Secure Digital (SD), Compact Flash (CF), Memory Stick, Multi-Media Card (MMC) and a network component.

0070Computing system <b>800</b> can also include an input/output (I/O) controller <b>812</b> that can be operatively coupled to processor <b>810</b> or it may be a separate component as shown. I/O controller <b>812</b> can be configured to control interactions with one or more I/O devices. I/O controller <b>812</b> can operate by exchanging data between processor <b>810</b> and the I/O devices that desire to communicate with processor <b>810</b>. The I/O devices and I/O controller <b>812</b> can communicate through a data link. The data link can be a one way link or a two way link. In some cases, I/O devices can be connected to I/O controller <b>812</b> through wireless connections. By way of example, a data link can correspond to PS/2, USB, Firewire, IR, RF, Bluetooth or the like.

0071Computing system <b>800</b> can include a display device <b>824</b> that can be operatively coupled to processor <b>810</b>. Display device <b>824</b> can be a separate component (peripheral device) or can be integrated with processor <b>810</b> and program storage block <b>802</b> to form a desktop computer (all in one machine), a laptop, handheld or tablet computing device of the like. Display device <b>824</b> can be configured to display a graphical user interface (GUI) including perhaps a pointer or cursor as well as other information to the user. By way of example, display device <b>824</b> can be any type of display including a liquid crystal display (LCD), an electroluminescent display (ELD), a field emission display (FED), a light emitting diode display (LED), an organic light emitting diode display (OLED) or the like.

0072Display device <b>824</b> can be coupled to display controller <b>826</b> that can be coupled to processor <b>810</b>. Processor <b>810</b> can send raw data to display controller <b>826</b>, and display controller <b>826</b> can send signals to display device <b>824</b>. Data can include voltage levels for a plurality of pixels in display device <b>824</b> to project an image. In some examples, processor <b>810</b> can be configured to process the raw data.

0073Computing system <b>800</b> can also include a touch screen <b>830</b> that can be operatively coupled to processor <b>810</b>. Touch screen <b>830</b> can be a combination of sensing device <b>832</b> and display device <b>824</b>, where the sensing device <b>832</b> can be a transparent panel that is positioned in front of display device <b>824</b> or integrated with display device <b>824</b>. In some cases, touch screen <b>830</b> can recognize touches and the position and magnitude of touches on its surface. Touch screen <b>830</b> can report the touches to processor <b>810</b>, and processor <b>810</b> can interpret the touches in accordance with its programming. For example, processor <b>810</b> can perform tap and event gesture parsing and can initiate a wake of the device or powering on one or more components in accordance with a particular touch.

0074Touch screen <b>830</b> can be coupled to a touch controller <b>840</b> that can acquire data from touch screen <b>830</b> and can supply the acquired data to processor <b>810</b>. In some cases, touch controller <b>840</b> can be configured to send raw data to processor <b>810</b>, and processor <b>810</b> processes the raw data. For example, processor <b>810</b> can receive data from touch controller <b>840</b> and can determine how to interpret the data. The data can include the coordinates of a touch as well as pressure exerted. In some examples, touch controller <b>840</b> can be configured to process raw data itself. That is, touch controller <b>840</b> can read signals from sensing points <b>834</b> located on sensing device <b>832</b> and turn them into data that the processor <b>810</b> can understand.

0075Touch controller <b>840</b> can include one or more microcontrollers such as microcontroller <b>842</b>, each of which can monitor one or more sensing points <b>834</b>. Microcontroller <b>842</b> can, for example, correspond to an application specific integrated circuit (ASIC), which works with firmware to monitor the signals from sensing device <b>832</b>, process the monitored signals, and report this information to processor <b>810</b>.

0076One or both display controller <b>826</b> and touch controller <b>840</b> can perform filtering and/or conversion processes. Filtering processes can be implemented to reduce a busy data stream to prevent processor <b>810</b> from being overloaded with redundant or non-essential data. The conversion processes can be implemented to adjust the raw data before sending or reporting them to processor <b>810</b>.

0077In some examples, sensing device <b>832</b> is based on capacitance. When two electrically conductive members come close to one another without actually touching, their electric fields can interact to form a capacitance. The first electrically conductive member can be one or more of the sensing points <b>834</b>, and the second electrically conductive member can be an object <b>890</b> such as a finger. As object <b>890</b> approaches the surface of touch screen <b>830</b>, a capacitance can form between object <b>890</b> and one or more sensing points <b>834</b> in close proximity to object <b>890</b>. By detecting changes in capacitance at each of the sensing points <b>834</b> and noting the position of sensing points <b>834</b>, touch controller <b>840</b> can recognize multiple objects, and determine the location, pressure, direction, speed and acceleration of object <b>890</b> as it moves across the touch screen <b>830</b>. For example, touch controller <b>840</b> can determine whether the sensed touch is a finger, tap, or an object covering the surface.

0078Sensing device <b>832</b> can be based on self-capacitance or mutual capacitance. In self-capacitance, each of the sensing points <b>834</b> can be provided by an individually charged electrode. As object <b>890</b> approaches the surface of the touch screen <b>830</b>, the object can capacitively couple to those electrodes in close proximity to object <b>890</b>, thereby stealing charge away from the electrodes. The amount of charge in each of the electrodes can be measured by the touch controller <b>840</b> to determine the position of one or more objects when they touch or hover over the touch screen <b>830</b>. In mutual capacitance, sensing device <b>832</b> can include a two layer grid of spatially separated lines or wires, although other configurations are possible. The upper layer can include lines in rows, while the lower layer can include lines in columns (e.g., orthogonal). Sensing points <b>834</b> can be provided at the intersections of the rows and columns. During operation, the rows can be charged, and the charge can capacitively couple from the rows to the columns. As object <b>890</b> approaches the surface of the touch screen <b>830</b>, object <b>890</b> can capacitively couple to the rows in close proximity to object <b>890</b>, thereby reducing the charge coupling between the rows and columns. The amount of charge in each of the columns can be measured by touch controller <b>840</b> to determine the position of multiple objects when they touch the touch screen <b>830</b>.

0079Computing system <b>800</b> can also include one or more light emitters such as light emitters <b>806</b> and <b>816</b> and one or more light sensors such as light sensor <b>804</b> proximate to skin <b>820</b> of a user. Light emitters <b>806</b> and <b>816</b> can be configured to generate light, and light sensor <b>804</b> can be configured to measure a light reflected or absorbed by skin <b>820</b>, vasculature, and/or blood of the user. Light sensor <b>804</b> can send measured raw data to processor <b>810</b>, and processor <b>810</b> can perform noise cancellation to determine the PPG signal and/or perfusion index. Processor <b>810</b> can dynamically activate light emitters and/or light sensors based on an application, user skin type, and usage conditions. In some examples, some light emitters and/or light sensors can be activated, while other light emitters and/or light sensors can be deactivated to conserve power, for example. In some examples, processor <b>810</b> can store the raw data and/or processed information in a ROM <b>818</b> or RAM <b>822</b> for historical tracking or for future diagnostic purposes.

0080In some examples, the light sensor(s) can measure light information and a processor can determine a PPG signal and/or perfusion index from the reflected, scattered, or absorbed light. Processing of the light information can be performed on the device as well. In some examples, processing of light information need not be performed on the device itself. <figref idref="DRAWINGS">FIG. <b>9</b></figref> illustrates an exemplary configuration in which a device is connected to a host according to examples of the disclosure. Host <b>910</b> can be any device external to device <b>900</b> including, but not limited to, any of the systems illustrated in <figref idref="DRAWINGS">FIGS. <b>1</b>A-<b>1</b>C</figref> or a server. Device <b>900</b> can be connected to host <b>910</b> through communications link <b>920</b>. Communications link <b>920</b> can be any connection including, but not limited to, a wireless connection and a wired connection. Exemplary wireless connections include Wi-Fi, Bluetooth, Wireless Direct, and Infrared. Exemplary wired connections include Universal Serial Bus (USB), FireWire, Thunderbolt, or any connection requiring a physical cable.

0081In operation, instead of processing light information from the light sensors on the device <b>900</b> itself, device <b>900</b> can send raw data <b>930</b> measured from the light sensors over communications link <b>920</b> to host <b>910</b>. Host <b>910</b> can receive raw data <b>930</b>, and host <b>910</b> can process the light information. Processing the light information can include canceling or reducing any noise due to artifacts and determining physiological signals such as a user's heart rate. Host <b>910</b> can include algorithms or calibration procedures to account for differences in a user's characteristics affecting PPG signal and perfusion index. Additionally, host <b>910</b> can include storage or memory for tracking a PPG signal and perfusion index history for diagnostic purposes. Host <b>910</b> can send the processed result <b>940</b> or related information back to device <b>900</b>. Based on the processed result <b>940</b>, device <b>900</b> can notify the user or adjust its operation accordingly. By offloading the processing and/or storage of the light information, device <b>900</b> can conserve space and power enabling device <b>900</b> to remain small and portable, as space that could otherwise be required for processing logic can be freed up on the device.

0082In some examples, an electronic device is disclosed. The electronic device may comprise: one or more light emitters configured to generate a plurality of light paths, wherein at least two of the plurality of light paths have separation distances with a predetermined relationship; one or more light sensors configured to detect the at least two light paths having the predetermined relationship; and logic coupled to the one or more light sensors and configured to detect a physiological signal from the at least two light paths. Additionally or alternatively to one or more examples disclosed above, in other examples, the predetermined relationship is a same separation distance. Additionally or alternatively to one or more examples disclosed above, in other examples, the logic is further configured to generate PPG signals and perfusion signals from the detected physiological signal. Additionally or alternatively to one or more examples disclosed above, in other examples, the predetermined relationship is different separation distances. Additionally or alternatively to one or more examples disclosed above, in other examples, the predetermined relationship is overlapping light paths. Additionally or alternatively to one or more examples disclosed above, the predetermined relationship is non-overlapping light paths. Additionally or alternatively to one or more examples disclosed above, in other examples, the predetermined relationship is co-located light paths. Additionally or alternatively to one or more examples disclosed above, in other examples, the predetermined relationship is non-co-located light paths. Additionally or alternatively to one or more examples disclosed above, in other examples, the logic is further configured to reduce noise in the plurality of light paths. Additionally or alternatively to one or more examples disclosed above, in other examples, the electronic device further comprises one or more first lenses disposed on the one or more light emitters. Additionally or alternatively to one or more examples disclosed above, in other examples, at least one of the one or more first lenses is a Fresnel lens or an image displacement film. Additionally or alternatively to one or more examples disclosed above, in other examples, at least one of the one or more first lenses includes an optical center placed in substantially a same location as light emitted from the one or more light emitters. Additionally or alternatively to one or more examples disclosed above, in other examples, the electronic device further comprises one or more second lenses disposed on the one or more light sensors. Additionally or alternatively to one or more examples disclosed above, in other examples, at least one of the one or more second lenses is an image displacement film, a brightness enhancement film, or a Fresnel lens. Additionally or alternatively to one or more examples disclosed above, in other examples, the electronic device further comprises: an optical isolation disposed between the one or more light emitters and the one or more light sensors; and a reflector disposed on at least one of the optical isolation, a window disposed on the one or more light emitters, and a window disposed on the one or more light sensors. Additionally or alternatively to one or more examples disclosed above, in other examples, at least one light sensor is partitioned into a plurality of sensing regions. Additionally or alternatively to one or more examples disclosed above, in other examples, at least two of the one or more light emitters emit light at different wavelengths. Additionally or alternatively to one or more examples disclosed above, in other examples, at least one light emitter is a green light emitting diode and at least one light emitter is an infrared light emitting diode.

0083In some examples, a method for forming an electronic device including one or more light emitters and one or more light sensors is disclosed. The method may comprise: emitting light from the one or more light emitters to generate a plurality of light paths, wherein at least two of the plurality of light paths have separation distances with a predetermined relationship; receiving light from the one or more light sensors; and determining a physiological signal from the received light. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises dynamically selecting one or more light paths based on at least one of a user characteristic and a usage condition. Additionally or alternatively to one or more examples disclosed above, in other examples, at least two of the plurality of light paths have a same separation distance, the method further comprises canceling or reducing a noise from the at least two of the plurality of light paths with the same separation distance. Additionally or alternatively to one or more examples disclosed above, in other examples, the at least two of the plurality of light paths including a first light path and a second light path, wherein the first light path has a first separation distance and the second light path has a second separation distance, and the first separation distance is shorter than the second separation distance, the method further comprises: determining a first physiological signal from the first light path; and determining a second physiological signal from the second light path. Additionally or alternatively to one or more examples disclosed above, in other examples, the first physiological signal is indicative of a photoplethysmographic signal and the second physiological signal is indicative of a perfusion index. Additionally or alternatively to one or more examples disclosed above, in other examples, the one or more light emitters includes a first set of light emitters and a second set of light emitters, the method further comprising: dynamically activating the first set of light emitters; and dynamically deactivating the second set of light emitters.

0084Although the disclosed examples have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the disclosed examples as defined by the appended claims.